Mitofusin1 in oocyte is essential for female fertility

Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging

Arf6 is a member of ADP-ribosylation factor (Arf) family, which is widely implicated in the regulation of multiple physiological processes including endocytic recycling, cytoskeletal organization, and membrane trafficking during mitosis. In this study, we investigated the potential relationship between Arf6 and aging-related oocyte quality, and its roles on organelle rearrangement and cytoskeleton dynamics in porcine oocytes. Arf6 expressed in porcine oocytes throughout meiotic maturation, and it decreased in aged oocytes. Disruption of Arf6 led to the failure of cumulus expansion and polar body extrusion. Further analysis indicated that Arf6 modulated ac-tubulin for meiotic spindle organization and microtubule stability. Besides, Arf6 regulated cofilin phosphorylation and fascin for actin assembly, which further affected spindle migration, indicating the roles of Arf6 on cytoskeleton dynamics. Moreover, the lack of Arf6 activity caused the dysfunction of Golgi and ER for protein synthesis and signal transduction. Mitochondrial dysfunction was also observed in Arf6-deficient porcine oocytes, which was supported by the increased ROS level and abnormal membrane potential. In conclusion, our results reported that insufficient Arf6 was related to aging-induced oocyte quality decline through spindle organization, actin assembly, and organelle rearrangement in porcine oocytes.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

The role of mitochondrial dynamics in oocyte and early embryo development

Mitochondrial dysfunction is widely implicated in various human diseases, through mechanisms that go beyond mitochondria's well-established role in energy generation. These dynamic organelles exert vital control over numerous cellular processes, including calcium regulation, phospholipid synthesis, innate immunity, and apoptosis. While mitochondria's importance is acknowledged in all cell types, research has revealed the exceptionally dynamic nature of the mitochondrial network in oocytes and embryos, finely tuned to meet unique needs during gamete and pre-implantation embryo development. Within oocytes, both the quantity and morphology of mitochondria can significantly change during maturation and post-fertilization. These changes are orchestrated by fusion and fission processes (collectively known as mitochondrial dynamics), crucial for energy production, content exchange, and quality control as mitochondria adjust to the shifting energy demands of oocytes and embryos. The roles of proteins that regulate mitochondrial dynamics in reproductive processes have been primarily elucidated through targeted deletion studies in animal models. Notably, impaired mitochondrial dynamics have been linked to female reproductive health, affecting oocyte quality, fertilization, and embryo development. Dysfunctional mitochondria can lead to fertility problems and can have an impact on the success of pregnancy, particularly in older reproductive age women.

Biallelic FANCA variants detected in sisters with isolated premature ovarian insufficiency

Premature ovarian insufficiency is a common form of female infertility affecting up to 4% of women and characterised by amenorrhea with elevated gonadotropin before the age of 40. Oocytes require controlled DNA breakage and repair for homologous recombination and the maintenance of oocyte integrity. Biallelic disruption of the DNA damage repair gene, Fanconi anemia complementation group A (FANCA), is a common cause of Fanconi anaemia, a syndrome characterised by bone marrow failure, cancer predisposition, physical anomalies and POI. There is ongoing dispute about the role of heterozygous FANCA variants in POI pathogenesis, with insufficient evidence supporting causation. Here, we have identified biallelic FANCA variants in French sisters presenting with POI, including a novel missense variant of uncertain significance and a likely pathogenic deletion that initially evaded detection. Functional studies indicated no discernible effect on DNA damage sensitivity in patient lymphoblasts. These novel FANCA variants add evidence that heterozygous loss of one allele is insufficient to cause DNA damage sensitivity and POI. We propose that intragenic deletions, that are relatively common in FANCA, may be missed without careful analysis, and could explain the presumed causation of heterozygous variants. Accurate variant curation is critical to optimise patient care and outcomes.

Bisphenol Z exposure inhibits oocyte meiotic maturation by rupturing mitochondrial function

The use of bisphenol A (BPA) has been restricted due to its endocrine-disrupting effects. As a widely used alternative to BPA today, environmental levels of bisphenol Z (BPZ) continue to rise and accumulate in humans. Oocyte quality is critical for a successful pregnancy. Nevertheless, the toxic impacts of BPZ on the maturation of mammalian oocytes remain unexplored. Therefore, the impacts of BPZ and BPA on oocyte meiotic maturation were compared in an in vitro mouse oocyte culture model. Exposure to 150 μM of both BPZ and BPA disrupted the assembly of the meiotic spindle and the alignment of chromosomes, and BPZ exerted stronger toxicological effects than BPA. Furthermore, BPZ resulted in aberrant expression of F-actin, preventing the formation of the actin cap. Mechanistically, BPZ exposure disrupted the mitochondrial localization pattern, reduced mitochondrial membrane potential and ATP content, leading to impaired mitochondrial function. Further studies revealed that BPZ exposure resulted in oxidative stress and altered expression of genes associated with anti-oxidative stress. Moreover, BPZ induced severe DNA damage and triggered early apoptosis in oocytes, accompanied by impaired lysosomal function. Overall, the data in this study suggest that BPZ is not a safe alternative to BPA. BPZ can trigger early apoptosis by affecting mitochondrial function and causing oxidative stress and DNA damage in oocytes. These processes disrupt cytoskeletal assembly, arrest the cell cycle, and ultimately inhibit oocyte meiotic maturation.

Levels of trace metals and their impact on oocyte: A review

Trace metals play a vital role in a variety of biological processes, but excessive amounts can be toxic and are receiving increasing attention. Trace metals in the environment are released from natural sources, such as rock weathering, volcanic eruptions, and other human activities, such as industrial emissions, mineral extraction, and vehicle exhaust. Lifestyle, dietary habits and environmental quality are the main sources of human exposure to trace metals, which play an important role in inducing human reproductive infertility. The purpose of this review is to summarize the distribution of various trace metals in oocyte and to identify the trace metals that may cause oocyte used in the design and execution of toxicological studies.

Mitochondrial morphology, distribution and activity during oocyte development

Mitochondria have a crucial role in cellular function and exhibit remarkable plasticity, adjusting both their structure and activity to meet the changing energy demands of a cell. Oocytes, female germ cells that become eggs, undergo unique transformations: the extended dormancy period, followed by substantial increase in cell size and subsequent maturation involving the segregation of genetic material for the next generation, present distinct metabolic challenges necessitating varied mitochondrial adaptations. Recent findings in dormant oocytes challenged the established respiratory complex hierarchies and underscored the extent of mitochondrial plasticity in long-lived oocytes. In this review, we discuss mitochondrial adaptations observed during oocyte development across three vertebrate species (Xenopus, mouse, and human), emphasising current knowledge, acknowledging limitations, and outlining future research directions.

A detailed review of pharmacology of MFN1 (mitofusion-1)-mediated mitochondrial dynamics: Implications for cellular health and diseases

The mitochondria are responsible for the production of cellular ATP, the regulation of cytosolic calcium levels, and the organization of numerous apoptotic proteins through the release of cofactors necessary for the activation of caspases. This level of functional adaptability can only be attained by sophisticated structural alignment. The morphology of the mitochondria does not remain unchanged throughout time; rather, it undergoes change as a result of processes known as fusion and fission. Fzo in flies, Fzo1 in yeast, and mitofusins in mammals are responsible for managing the outer mitochondrial membrane fusion process, whereas Mgm1 in yeast and optic atrophy 1 in mammals are responsible for managing the inner mitochondrial membrane fusion process. The fusion process is composed of two phases. MFN1, a GTPase that is located on the outer membrane of the mitochondria, is involved in the process of linking nearby mitochondria, maintaining the potential of the mitochondrial membrane, and apoptosis. This article offers specific information regarding the functions of MFN1 in a variety of cells and organs found in living creatures. According to the findings of the literature review, MFN1 plays an important part in a number of diseases and organ systems; nevertheless, the protein's function in other disease models and cell types has to be investigated in the near future so that it can be chosen as a promising marker for the therapeutic and diagnostic potentials it possesses. Overall, the major findings of this review highlight the pivotal role of mitofusin (MFN1) in regulating mitochondrial dynamics and its implications across various diseases, including neurodegenerative disorders, cardiovascular diseases, and metabolic syndromes. Our review identifies novel therapeutic targets within the MFN1 signaling pathways and underscores the potential of MFN1 modulation as a promising strategy for treating mitochondrial-related diseases. Additionally, the review calls for further research into MFN1's molecular mechanisms to unlock new avenues for clinical interventions, emphasizing the need for targeted therapies that address MFN1 dysfunction.

3-Methyl-4-nitrophenol Exposure Deteriorates Oocyte Maturation by Inducing Spindle Instability and Mitochondrial Dysfunction

3-methyl-4-nitrophenol (PNMC), a well-known constituent of diesel exhaust particles and degradation products of insecticide fenitrothion, is a widely distributed environmental contaminant. PNMC is toxic to the female reproductive system; however, how it affects meiosis progression in oocytes is unknown. In this study, in vitro maturation of mouse oocytes was applied to investigate the deleterious effects of PNMC. We found that exposure to PNMC significantly compromised oocyte maturation. PNMC disturbed the spindle stability; specifically, it decreased the spindle density and increased the spindle length. The weakened spindle pole location of microtubule-severing enzyme Fignl1 may result in a defective spindle apparatus in PNMC-exposed oocytes. PNMC exposure induced significant mitochondrial dysfunction, including mitochondria distribution, ATP production, mitochondrial membrane potential, and ROS accumulation. The mRNA levels of the mitochondria-related genes were also significantly impaired. Finally, the above-mentioned alterations triggered early apoptosis in the oocytes. In conclusion, PNMC exposure affected oocyte maturation and quality through the regulation of spindle stability and mitochondrial function.

Peptide derived from RAGE efficiently improves oocyte development through attenuating oxidative stress in oocytes of mice with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common and complex endocrine disorder in reproductive-aged women that frequently leads to infertility due to poor oocyte quality. In this study, we identified a new active peptide (advanced glycation end products receptors RAGE344-355 ) from PCOS follicular fluid using mass spectrometry. We found that supplementing PCOS-like mouse oocytes with RAGE344-355 attenuated both meiotic defects and oxidative stress levels, ultimately preventing developmental defects. Additionally, our results suggest that RAGE344-355 may interact with eEF1a1 to mitigate oxidative meiotic defects in PCOS-like mouse oocytes. These findings highlight the potential for further clinical development of RAGE344-355 as a potent supplement and therapeutic option for women with PCOS. This research addresses an important clinical problem and offers promising opportunities for improving oocyte quality in PCOS patients.

Effects of reactive oxygen species and mitochondrial dysfunction on reproductive aging

Mitochondria, the versatile organelles crucial for cellular and organismal viability, play a pivotal role in meeting the energy requirements of cells through the respiratory chain located in the inner mitochondrial membrane, concomitant with the generation of reactive oxygen species (ROS). A wealth of evidence derived from contemporary investigations on reproductive longevity strongly indicates that the aberrant elevation of ROS level constitutes a fundamental factor in hastening the aging process of reproductive systems which are responsible for transmission of DNA to future generations. Constant changes in redox status, with a pro-oxidant shift mainly through the mitochondrial generation of ROS, are linked to the modulation of physiological and pathological pathways in gametes and reproductive tissues. Furthermore, the quantity and quality of mitochondria essential to capacitation and fertilization are increasingly associated with reproductive aging. The article aims to provide current understanding of the contributions of ROS derived from mitochondrial respiration to the process of reproductive aging. Moreover, understanding the impact of mitochondrial dysfunction on both female and male fertility is conducive to finding therapeutic strategies to slow, prevent or reverse the process of gamete aging, and thereby increase reproductive longevity.

Arachidonic acid inhibit granulosa cell function by affecting metabolic function of liver in brown adipose transplantation rats

BACKGROUND

Polycystic ovary syndrome (PCOS) is a gynecological endocrine disease and could be considered a metabolic disease because it is often accompanied by obesity and insulin resistance. Brown adipose tissue (BAT) transplantation has been shown to be effective in treating PCOS rats.

RESULTS

The study demonstrated that BAT successfully recovered the reproductive and metabolic phenotype of PCOS rats. The disorder estrous cycle, abnormal hyperglycemia and the expression of liver factors were improved. Differentially expressed metabolites were analyzed, among them, arachidonic acid may play a role in inhibiting cell proliferation, enhancing oxidative stress reaction, promoting estrogen expression, and reducing progesterone level in KGN cells.

CONCLUSION

Our findings suggest that BAT transplantation may be a therapeutic strategy for PCOS by changing the expression of some cytokines and metabolites. Differentially expressed metabolites might be crucially important for the pathogenesis of PCOS.

NAMPT regulates mitochondria function and lipid metabolism during porcine oocyte maturation

Oocyte maturation defect can lead to maternal reproduction disorder. NAMPT is a rate-limiting enzyme in mammalian NAD+ biosynthesis pathway, which can regulate a variety of cellular metabolic processes including glucose metabolism and DNA damage repair. However, the function of NAMPT in porcine oocytes remains unknown. In this study, we showed that NAMPT involved into multiple cellular events during oocyte maturation. NAMPT expressed during all stages of porcine oocyte meiosis, and inhibition of NAMPT activity caused the cumulus expansion and polar body extrusion defects. Mitochondrial dysfunction was observed in NAMPT-deficient porcine oocytes, which showed decreased membrane potential, ATP and mitochondrial DNA content, increased oxidative stress level and apoptosis. We also found that NAMPT was essential for spindle organization and chromosome arrangement based on Ac-tubulin. Moreover, lack of NAMPT activity caused the increase of lipid droplet and affected the imbalance of lipogenesis and lipolysis. In conclusion, our study indicated that lack of NAMPT activity affected porcine oocyte maturation through its effects on mitochondria function, spindle assembly and lipid metabolism.

SIRT3 Regulates Levels of Deacetylated SOD2 to Prevent Oxidative Stress and Mitochondrial Dysfunction During Oocyte Maturation in Pigs

Mammalian oocyte maturation relies on mitochondrial ATP production, but this can lead to damaging reactive oxygen species (ROS). SIRT3, a mitochondrial sirtuin, plays a critical role in regulating mitochondrial redox balance in mouse oocytes under stress; however, its specific roles in porcine oocytes remain unclear. In this study, we utilized the SIRT3 inhibitor 3-TYP to investigate SIRT3's importance in porcine oocyte maturation. Our findings revealed that SIRT3 is expressed in porcine oocytes and its inhibition leads to maturation failure. This was evident through reduced polar body extrusion, arrested cell cycle, as well as disrupted spindle organization and actin distribution. Furthermore, SIRT3 inhibition resulted in a decrease in mitochondrial DNA copy numbers, disruption of mitochondrial membrane potential, and reduced ATP levels, all indicating impaired mitochondrial function in porcine oocytes. Additionally, the primary source of damaged mitochondria was associated with decreased levels of deacetylated superoxide dismutase 2 (SOD2) after SIRT3 inhibition, which led to ROS accumulation and oxidative stress-induced apoptosis. Taken together, our results suggest that SIRT3 regulates the levels of deacetylated SOD2 to maintain redox balance and preserve mitochondrial function during porcine oocyte maturation, with potential implications for improving pig reproduction.

Mitochondrial GTP metabolism controls reproductive aging in C. elegans

Healthy mitochondria are critical for reproduction. During aging, both reproductive fitness and mitochondrial homeostasis decline. Mitochondrial metabolism and dynamics are key factors in supporting mitochondrial homeostasis. However, how they are coupled to control reproductive health remains unclear. We report that mitochondrial GTP (mtGTP) metabolism acts through mitochondrial dynamics factors to regulate reproductive aging. We discovered that germline-only inactivation of GTP- but not ATP-specific succinyl-CoA synthetase (SCS) promotes reproductive longevity in Caenorhabditis elegans. We further identified an age-associated increase in mitochondrial clustering surrounding oocyte nuclei, which is attenuated by GTP-specific SCS inactivation. Germline-only induction of mitochondrial fission factors sufficiently promotes mitochondrial dispersion and reproductive longevity. Moreover, we discovered that bacterial inputs affect mtGTP levels and dynamics factors to modulate reproductive aging. These results demonstrate the significance of mtGTP metabolism in regulating oocyte mitochondrial homeostasis and reproductive longevity and identify mitochondrial fission induction as an effective strategy to improve reproductive health.

Ferulic Acid Enhances Oocyte Maturation and the Subsequent Development of Bovine Oocytes

Improving the quality of oocytes matured in vitro is integral to enhancing the efficacy of in vitro embryo production. Oxidative stress is one of the primary causes of quality decline in oocytes matured in vitro. In this study, ferulic acid (FA), a natural antioxidant found in plant cell walls, was investigated to evaluate its impact on bovine oocyte maturation and subsequent embryonic development. Bovine cumulus-oocyte complexes (COCs) were treated with different concentrations of FA (0, 2.5, 5, 10, 20 μM) during in vitro maturation (IVM). Compared to the control group, supplementation with 5 μM FA significantly enhanced the maturation rates of bovine oocytes and the expansion of the cumulus cells area, as well as the subsequent cleavage and blastocyst formation rates after in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT). Furthermore, FA supplementation was observed to effectively decrease the levels of ROS in bovine oocytes and improve their mitochondrial function. Our experiments demonstrate that FA can maintain the levels of antioxidants (GSH, SOD, CAT) in oocytes, thereby alleviating the oxidative stress induced by H2O2. RT-qPCR results revealed that, after FA treatment, the relative mRNA expression levels of genes related to oocyte maturation (GDF-9 and BMP-15), cumulus cell expansion (HAS2, PTX3, CX37, and CX43), and embryo pluripotency (OCT4, SOX2, and CDX2) were significantly increased. In conclusion, these findings demonstrate that FA supplementation during bovine oocyte IVM can enhance oocyte quality and the developmental potential of subsequent embryos.

NLRP14 Safeguards Calcium Homeostasis via Regulating the K27 Ubiquitination of Nclx in Oocyte-to-Embryo Transition

Sperm-induced Ca2+ rise is critical for driving oocyte activation and subsequent embryonic development, but little is known about how lasting Ca2+ oscillations are regulated. Here it is shown that NLRP14, a maternal effect factor, is essential for keeping Ca2+ oscillations and early embryonic development. Few embryos lacking maternal NLRP14 can develop beyond the 2-cell stage. The impaired developmental potential of Nlrp14-deficient oocytes is mainly caused by disrupted cytoplasmic function and calcium homeostasis due to altered mitochondrial distribution, morphology, and activity since the calcium oscillations and development of Nlrp14-deficient oocytes can be rescued by substitution of whole cytoplasm by spindle transfer. Proteomics analysis reveal that cytoplasmic UHRF1 (ubiquitin-like, containing PHD and RING finger domains 1) is significantly decreased in Nlrp14-deficient oocytes, and Uhrf1-deficient oocytes also show disrupted calcium homeostasis and developmental arrest. Strikingly, it is found that the mitochondrial Na+ /Ca2+ exchanger (NCLX) encoded by Slc8b1 is significantly decreased in the Nlrp14mNull oocyte. Mechanistically, NLRP14 interacts with the NCLX intrinsically disordered regions (IDRs) domain and maintain its stability by regulating the K27-linked ubiquitination. Thus, the study reveals NLRP14 as a crucial player in calcium homeostasis that is important for early embryonic development.

Premature ovarian insufficiency: a review on the role of oxidative stress and the application of antioxidants

Normal levels of reactive oxygen species (ROS) play an important role in regulating follicular growth, angiogenesis and sex hormone synthesis in ovarian tissue. When the balance between ROS and antioxidants is disrupted, however, it can cause serious consequences of oxidative stress (OS), and the quantity and quality of oocytes will decline. Therefore, this review discusses the interrelationship between OS and premature ovarian insufficiency (POI), the potential mechanisms and the methods by which antioxidants can improve POI through controlling the level of OS. We found that OS can mediate changes in genetic materials, signal pathways, transcription factors and ovarian microenvironment, resulting in abnormal apoptosis of ovarian granulosa cells (GCs) and abnormal meiosis as well as decreased mitochondrial Deoxyribonucleic Acid(mtDNA) and other changes, thus accelerating the process of ovarian aging. However, antioxidants, mesenchymal stem cells (MSCs), biological enzymes and other antioxidants can delay the disease process of POI by reducing the ROS level in vivo.

Growth Hormone Promotes Oocyte Maturation In Vitro by Protecting Mitochondrial Function and Reducing Apoptosis

Some studies have been conducted to explore the influence of growth hormone (GH) on oocytes in in vitro maturation (IVM); however, previous studies reporting showed different results, and the specific mechanisms were not clear. In the present study, GH supplementation improved oocyte maturation rate. The rate of germinal vesicle breakdown (GVBD) in the GH group was 83.9%, which was significantly higher than that (72.1%) in the control group (p = 0.001). The maturation rate of the GH group (79.2%) was significantly higher than that (65.4%) of the control group (p = 0.000). The fertilization (68.6 vs. 59.3%) and blastocyst (30 vs. 25.3%) rates showed an increasing trend in the GH group compared to those in controls. The dynamic parameters of nuclear maturation of oocytes were recorded by time-lapse monitoring system; oocytes in the GH group completed nuclear maturation earlier than did those in the control group. GH reduced cAMP levels to promote oocyte maturation. Single-cell RNA sequencing analysis revealed that the majority of differentially expressed genes (DEGs) involved in mitochondrial oxidative phosphorylation was upregulated in the GH group. Furthermore, the mitochondrial membrane potential of oocytes significantly increased, and the levels of intracellular reactive oxygen species (ROS) and Ca2+ largely decreased in the GH group. Finally, single-oocyte transcriptome analysis indicated that GH decreased the expression of apoptosis-related genes in oocytes. GH treatment reduced the expression of γH2AX and caspase-3. Therefore, GH improves the developmental potential of immature oocytes by reducing cAMP levels more rapidly within 0.5 h, protecting mitochondrial function, and reducing DNA damage and apoptosis.

miR-27a-3p relieves heat stress-induced mitochondrial damage and aberrant milk protein synthesis through MEK/ERK pathway in BMECs

With global warming, heat stress has become a primary factor that compromises the health and milk quality of dairy cows. Here, we investigated the function and underlying regulatory mechanism of miR-27a-3p in bovine mammary epithelial cells (BMECs) under heat-stress conditions. The current study showed that miR-27a-3p could prevent heat stress-induced BMEC oxidative stress and mitochondrial damage by regulating the balance between mitochondrial fission and fusion processes. Importantly, we found that miR-27a-3p could increase cell proliferation under heat stress conditions by regulating the MEK/ERK pathway and cyclin D1/E1. Interestingly, miR-27a-3p is also involved in the regulation of milk protein synthesis-related protein expression, such as CSN2 and ELF5. Inhibition of the MEK/ERK signaling pathway by AZD6244 blocked the regulatory function of miR-27a-3p in cell proliferation and milk protein synthesis in BMECs under heat stress conditions. Our findings demonstrated that miR-27a-3p protects BMECs from heat stress-induced oxidative stress and mitochondrial damage through the MEK/ERK pathway, thereby promoting BMECs proliferation and lactation in dairy cows. The potential regulatory mechanism of miR-27a-3p in attenuating heat stress-induced apoptosis and lactation defect in BMECs.

Oxr1a prevents the premature ovarian failure by regulating oxidative stress and mitochondrial function in zebrafish

Premature ovarian failure (POF) is characterized as the ovarian dysfunction and defective oocyte development. In POF patients, ROS level is reported to be significantly higher than normal individuals. However, the involvement of oxidative stress in POF and the regulatory mechanisms underlying the antioxidative process in oocyte development remain largely unknown. Here, we discover that oxidation resistance 1a (Oxr1a), the ortholog of mammalian Oxr1, protects the oocytes of female zebrafish against oxidative stress and thus represses the POF phenotype. Oxr1a was widely expressed in oocytes at different developmental stages, of which the mRNA expression levels were significantly upregulated upon follicle activation and oocyte maturation. Oxr1a knockout exacerbated the POF phenotype, as evidenced by the decreased number and quality of oocytes. Moreover, the oocytes of oxr1a knockout zebrafish exhibited excessive ROS, increased mitochondrial DNA damage, reduced mitochondria, and abnormal morphology. Mechanistically, instead of decomposing ROS directly, Oxr1a participated in the process of oxidative stress through regulating the mRNA expression levels of the key antioxidant enzymes Cat and Sod1. Moreover, treatment with antioxidant N-Acetyl-l-cysteine attenuated the mitochondrial oxidative damage and improved the fertility of mutant females, indicating that Oxr1a may mediates the Sod1/Cat pathway to metabolize the intracellular ROS and avoid the mitochondrial oxidative damage, thus ensuring the normal development and maturation of oocytes. Taken together, these findings are useful for the elucidation of molecular mechanisms underlying the oxidative damage in oocytes and beneficial to the clinical therapeutics of POF.

Mitochondrial GTP Metabolism Regulates Reproductive Aging

Healthy mitochondria are critical for reproduction. During aging, both reproductive fitness and mitochondrial homeostasis decline. Mitochondrial metabolism and dynamics are key factors in supporting mitochondrial homeostasis. However, how they are coupled to control reproductive health remains unclear. We report that mitochondrial GTP metabolism acts through mitochondrial dynamics factors to regulate reproductive aging. We discovered that germline-only inactivation of GTP- but not ATP-specific succinyl-CoA synthetase (SCS), promotes reproductive longevity in Caenorhabditis elegans. We further revealed an age-associated increase in mitochondrial clustering surrounding oocyte nuclei, which is attenuated by the GTP-specific SCS inactivation. Germline-only induction of mitochondrial fission factors sufficiently promotes mitochondrial dispersion and reproductive longevity. Moreover, we discovered that bacterial inputs affect mitochondrial GTP and dynamics factors to modulate reproductive aging. These results demonstrate the significance of mitochondrial GTP metabolism in regulating oocyte mitochondrial homeostasis and reproductive longevity and reveal mitochondrial fission induction as an effective strategy to improve reproductive health.

Mitochondrial E3 ubiquitin ligase MARCH5 is required for mouse oocyte meiotic maturation†

As the most abundant organelles in oocytes, mitochondria play an important role in maintaining oocyte quality. Here, we report that March5, encoding a mitochondrial ubiquitin ligase that promotes mitochondrial elongation, plays a critical role in mouse oocyte meiotic maturation via regulating mitochondrial function. The subcellular localization of MARCH5 was similar to the mitochondrial distribution during mouse oocyte meiotic progression. Knockdown of March5 caused decreased ratios of the first polar body extrusion. March5-siRNA injection resulted in oocyte mitochondrial dysfunctions, manifested by increased reactive oxygen species, decreased ATP content as well as decreased mitochondrial membrane potential, leading to reduced ability of spindle formation and an increased ratio of kinetochore-microtubule detachment. Further study showed that the continuous activation of the spindle assembly checkpoint and the failure of Cyclin B1 degradation caused MI arrest and first polar body (PB1) extrusion failure in March5 knockdown oocytes. Taken together, our results demonstrated that March5 plays an essential role in mouse oocyte meiotic maturation, possibly via regulation of mitochondrial function and/or ubiquitination of microtubule dynamics- or cell cycle-regulating proteins.

Targeted Deletion of Mitofusin 1 and Mitofusin 2 Causes Female Infertility and Loss of Follicular Reserve

Mitochondria are dynamic organelles that regulate their size, shape, and morphology through mechanisms called fusion and fission, to continually adapt themselves to their bioenergetic environment. These mechanisms play a critical role to maintain the mitochondrial function under metabolic and environmental stress. Mitofusin 1 (MFN1) and mitofusin 2 (MFN2) are transmembrane GTPases that regulate mitochondrial fusion mechanism and are required for the maintenance of cellular homeostasis. In this study, we aimed to determine the role of mitofusins in female reproductive competence and senescence using a mouse model with oocyte-specific double deletion of Mfn1 and Mfn2, eliminating the potential functional redundancy of these two proteins. Oocyte-specific targeted double deletion of Mfn1 and Mfn2 in mice resulted in female infertility associated with impaired follicular development and oocyte maturation. It also resulted in altered mitochondrial dynamics and mitochondrial dysfunction. Lack of Mfn1 and Mfn2 in oocytes resulted in accelerated follicular depletion and impaired oocyte quality which are consistent with phenotype of reproductive aging.

Downregulation of PI3K/AKT/mTOR Pathway in Juglone-Treated Bovine Oocytes

We have previously reported that juglone, a natural compound found in Juglandaceae with a wide range of biological activities, can reduces the developmental competence of bovine oocytes. In the current study, we investigated the possible mechanisms behind the toxicity of juglone and the relationship with PI3K/AKT/mTOR signaling during the in vitro maturation (IVM) of oocytes. Results show that oocyte exposure to juglone was associated with a significant decrease in filamentous actin (F-actin) accumulation. The RT-qPCR showed downregulation of the meiosis progression indicator GSK-3A, oocyte development marker BMP15, mitochondria fusion controlling MFN1, oxidative stress-related OGG1, and histone methylation-related EZH1, EZH2, SUZ12, G9a, and SUV39H2 genes in juglone-treated oocytes. In addition, glycolysis- (PFK1 and GLUT1), ATP synthesis- (ATPase8 and ATP5F1B), and OXPHOS-specific markers (SDHA and SDHD), as well as the oocyte survival regulators (SOD2, VEGF, and MAPK1) significantly decreased upon juglone treatment. Moreover, lower expression of PI3K, AKT, and mTOR was observed at the transcriptional and/or translational level(s). The autophagy markers LC3B and beclin-1 as well as the DNA damage-specific marker 8-OxoG displayed overexpression in juglone-exposed oocytes. Taken together, our results show that administration of juglone during the IVM can reduce the quality and developmental health of bovine oocytes through downregulation of the PI3K/AKT/mTOR pathway and its downstream signaling cascades.

Perfluorooctanoic acid exposure in vivo perturbs mitochondrial metabolic during oocyte maturation

Perfluorooctanoic acid (PFOA), a member of a group of polyfluorinated and perfluorinated alkyl substances (PFAS), is associated with adverse pregnancy outcomes in mammals. However, the effects of in vivo exposure to PFOA on the female reproductive system and the underlying mechanisms remain unclear. In our study, we constructed a mouse model to investigate whether low-dose PFOA (1 mg/kg/day) or high-dose PFOA (5 mg/kg/day) affect meiosis maturation of oocytes and the potential mechanisms that may be associated with oocyte maturation disorder. Our results indicate that low-dose and high-dose PFOA can lead to impaired oocyte maturation, which is manifested by decreased rate of embryonic foam rupture and first polar body extrusion. Moreover, PFOA exposure harmed the mitochondrial metabolic, resulting in low levels of ATP contents, high reactive oxygen species, aberrant mitochondrial membrane potential. In addition, the proportion of DNA damage marker γ-H2AX was also significantly increased in PFOA exposure oocytes. These changes lead to abnormal arrangements of the spindle and chromosomes during oocyte maturation. In conclusion, our results for the first time illustrated that exposure to PFOA in vivo in female mice impaired the meiosis maturation of oocytes, which provided a basis for studying the mechanism of PFOA reproductive toxicity in female mammals.

Ovarian aging: mechanisms and intervention strategies

Ovarian reserve is essential for fertility and influences healthy aging in women. Advanced maternal age correlates with the progressive loss of both the quantity and quality of oocytes. The molecular mechanisms and various contributing factors underlying ovarian aging have been uncovered. In this review, we highlight some of critical factors that impact oocyte quantity and quality during aging. Germ cell and follicle reserve at birth determines reproductive lifespan and timing the menopause in female mammals. Accelerated diminishing ovarian reserve leads to premature ovarian aging or insufficiency. Poor oocyte quality with increasing age could result from chromosomal cohesion deterioration and misaligned chromosomes, telomere shortening, DNA damage and associated genetic mutations, oxidative stress, mitochondrial dysfunction and epigenetic alteration. We also discuss the intervention strategies to delay ovarian aging. Both the efficacy of senotherapies by antioxidants against reproductive aging and mitochondrial therapy are discussed. Functional oocytes and ovarioids could be rejuvenated from pluripotent stem cells or somatic cells. We propose directions for future interventions. As couples increasingly begin delaying parenthood in life worldwide, understanding the molecular mechanisms during female reproductive aging and potential intervention strategies could benefit women in making earlier choices about their reproductive health.

Oocyte-Specific Knockout of Histone Lysine Demethylase KDM2a Compromises Fertility by Blocking the Development of Follicles and Oocytes

The methylation status of histones plays a crucial role in many cellular processes, including follicular and oocyte development. Lysine-specific demethylase 2a (KDM2a) has been reported to be closely associated with gametogenesis and reproductive performance, but the specific function and regulatory mechanism have been poorly characterized in vivo. We found KDM2a to be highly expressed in growing follicles and oocytes of mice in this study. To elucidate the physiological role of Kdm2a, the zona pellucida 3-Cre (Zp3-Cre)/LoxP system was used to generate an oocyte Kdm2a conditional knockout (Zp3-Cre; Kdm2a^flox/flox, termed Kdm2a cKO) model. Our results showed that the number of pups was reduced by approximately 50% in adult Kdm2a cKO female mice mating with wildtype males than that of the control (Kdm2a^flox/flox) group. To analyze the potential causes, the ovaries of Kdm2a cKO mice were subjected to histological examination, and results indicated an obvious difference in follicular development between Kdm2a cKO and control female mice and partial arrest at the primary antral follicle stage. The GVBD and matured rates of oocytes were also compromised after conditional knockout Kdm2a, and the morphological abnormal oocytes increased. Furthermore, the level of 17β-estradiol of Kdm2a cKO mice was only 60% of that in the counterparts, and hormone sensitivity decreased as the total number of ovulated and matured oocytes decreased after superovulation. After deletion of Kdm2a, the patterns of H3K36me2/3 in GVBD-stage oocytes were remarkedly changed. Transcriptome sequencing showed that the mRNA expression profiles in Kdm2a cKO oocytes were significantly different, and numerous differentially expressed genes were involved in pathways regulating follicular and oocyte development. Taken together, these results indicated that the oocyte-specific knockout Kdm2a gene led to female subfertility, suggesting the crucial role of Kdm2a in epigenetic modification and follicular and oocyte development.

Miro1 regulates mitochondrial homeostasis and meiotic resumption of mouse oocyte

Miro1, a mitochondrial Rho GTPase1, is a kind of mitochondrial outer membrane protein involved in the regulation of mitochondrial anterograde transport and its subcellular distribution. Mitochondria influence reproductive processes of mammals in some aspects. Mitochondria are important for oocyte maturation, fertilization and embryonic development. The purpose of this study was to evaluate whether Miro1 regulates mouse oocyte maturation by altering mitochondrial homeostasis. We showed that Miro1 was expressed in mouse oocyte at different maturation stages. Miro1 mainly distributed in the cytoplasm and around the spindle during oocyte maturation. Small interference RNA-mediated Miro1 depletion caused significantly abnormal distribution of mitochondria and endoplasmic reticulum as well as mitochondrial dysfunction, resulting in severely impaired germinal vesicle breakdown (GVBD) of mouse oocytes. For those oocytes which went through GVBD in the Miro1-depleted group, part of them were inhibited in meiotic prophase I stage with abnormal chromosome arrangement and scattered spindle length. Our results suggest that Miro1 is essential for maintaining the maturation potential of mouse oocyte.

Integrated mRNA and miRNA Expression Profile Analysis of Female and Male Gonads in Acrossocheilus fasciatus

MicroRNAs (miRNAs) are regarded as key regulators in gonadal development and sex determination in diverse organisms. However, the functions of miRNAs in gonads of Acrossocheilus fasciatus, an economically important freshwater species in the south of China, are still unclear. Here, high-throughput sequencing was performed to investigate the mRNA and miRNAs on gonads of A. fasciatus. In total, 49,447 unigenes were obtained, including 11,635 differentially expressed genes (DEGs), among which 4147 upregulated genes and 7488 downregulated genes in the testis compared to the ovary, while 300 (237 known, and 63 novel) miRNAs with 36 differentially expressed miRNAs (DEMs) were identified, from which 17 upregulated and 19 downregulated DEMs. GO and KEGG enrichment analysis were performed to analyze the potential biological functions of DEGs and DEMs. Using qRT-PCR, 9 sex-related genes and 9 miRNAs were selected to verify the sequencing data. By dual-luciferase reporter assay, miR-22a-5p and miR-22b-5p interaction with piwil1, and miR-10d-5p interaction with piwil2 were identified. These findings could provide a reference for miRNA-regulated sex control of A. fasciatus and may reveal new insights into aquaculture and breeding concepts.

Glyphosate exposure deteriorates oocyte meiotic maturation via induction of organelle dysfunctions in pigs

Background

Recently, defects in mammalian oocytes maturation induced by environmental pollution results in the decreasing animal reproduction. Animal exposed to glyphosate is largely unavoidable because glyphosate is one of the most widely used herbicide worldwide due to its high-efficiency and broad-spectrum effects, which causes glyphosate an environmental contaminant found in soil, water and food. During the last few years, the growing and wider use of glyphosate has raised great concerns about its effects of reproductive toxicity. In this study, using porcine models, we investigated effects of glyphosate on organelle functions during oocyte meiosis.

Results

The results showed glyphosate exposure disrupted porcine oocyte maturation. Expression levels of cumulus expansion-related genes were interfered, further indicating the meiotic defects. The damaging effects were mediated by destruction of mitochondrial distribution and functions, which induced ROS accumulation and oxidative stress, also indicated by the decreased mRNA expression of related antioxidant enzyme genes. We also found an interference of endoplasmic reticulum (ER) distribution, disturbance of Ca²⁺ homeostasis, as well as fluctuation of ER stress, showing with the reduced ER stress-related mRNA or protein expression, which could indicate the dysfunction of ER for protein processing and signal transduction in glyphosate-exposed oocytes. Moreover, glyphosate exposure induced the disruption of lysosome function for autophagy, showing with the decrease of LAMP2 expression and autophagy-related genes mRNA expression. Additionally, our data showed the distribution of Golgi apparatus and the functions of ribosome were disturbed after glyphosate exposure, which might affect protein synthesis and transport.

Conclusions

Collectively, our study showed that exposed to glyphosate could affect animal reproduction by compromising the quality of oocytes through its wide toxic effects on organelle functions.

LARS2 Regulates Apoptosis via ROS-Mediated Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Ovarian Granulosa Cells

Several studies have indicated that mutations of LARS2 are associated with premature ovarian insufficiency (POI). However, the pathogenic mechanism of LARS2 in POI has not been reported yet. In the present study, the expression levels of LARS2 and E2F1 in granulosa cells (GCs) of POI patients were examined. CCK-8 and Edu assay were performed to determine the effect of LARS2 on cell proliferation. Apoptosis rate, mitochondrial membrane potential, reactive oxygen species (ROS), and cytoplasm Ca²⁺ levels were analyzed by flow cytometry. Western blot was conducted to evaluate the expression level of genes affected by LARS2. Transmission electron microscopy (TEM) was used to observe mitochondrial structure in GCs. Chromatin immunoprecipitation (ChIP) was used to evaluate the regulatory effect of E2F1 on Mfn-2 expression. Our results showed that LARS2 expression was downregulated in GCs of POI patients. Silencing of LARS2 inhibited cell proliferation and promoted the apoptosis of GCs. Meanwhile, LARS2 knockdown could induce mitochondrial dysfunction and accumulation of ROS levels. Moreover, ROS was found to be involved in the antiproliferation, proapoptotic, and endoplasmic reticulum (ER) stress effects of LARS2 knockdown. Furthermore, we also found that the expression level of E2F1 was positively correlated with LARS2. In addition, E2F1 could bind at the -61/-46 region of Mfn-2 promoter and regulated MFN-2 transcription. These findings demonstrated that LARS2 could promote the expression of E2F1. E2F1 mediated the effect of LARS2 on Mfn-2 expression via targeting the promoter region of Mfn-2, in which subsequently regulated cell proliferation and apoptosis, which resulted in the etiology of POI. This study will provide useful information for further investigations on the LARS2 in the occurrence of POI.

Reactive oxygen species-induced SIAH1 promotes granulosa cells' senescence in premature ovarian failure

Reactive oxygen species (ROS) exposure triggers granulosa cells' (GCs) senescence, which is an important causal factor for premature ovarian failure (POF). However, underlying mechanism in this process remains unknown. In our study, we observed increased ROS levels in POF ovarian tissues, POF patient follicular GCs and cyclophosphamide (CTX) pretreated GCs. Correspondingly, increased SIAH1, reduced TRF2 and GC senescence were also found in these cases. Silencing of SIAH1 rescued ROS‐induced TRF2 reduction and cell senescence in GCs. Moreover, SIAH1 co‐localized with TRF2 in the cytoplasm, facilitating its ubiquitination degradation, further leading to telomere abnormalities in GCs. In conclusion, our findings indicate that ROS induces telomere abnormalities by augmenting SIAH1‐mediated TRF2 degradation, leading to cell senescence in GCs in POF processing.

Phosphoglycerate mutase family member 5 maintains oocyte quality via mitochondrial dynamic rearrangement during aging

Decline in ovarian reserve with aging is associated with reduced fertility and the development of metabolic abnormalities. Once mitochondrial homeostasis is imbalanced, it may lead to poor reproductive cell quality and aging. However, Phosphoglycerate translocase 5 (PGAM5), located in the mitochondrial membrane, is associated with necroptosis, apoptosis, and mitophagy, although the underlying mechanisms associated with ovarian aging remain unknown. Therefore, we attempted to uncover whether the high phosphoglycerate mutant enzyme family member 5 (PGAM5) expression is associated with female infertility in cumulus cells, and aims to find out the underlying mechanism of action of PGAM5. We found that PGAM5 is highly expressed and positively associated with aging, and has the potential to help maintain and regulate mitochondrial dynamics and metabolic reprogramming in aging granulosa cells, ovaries of aged female mice, and elderly patients. PGAM5 undergoes activation in the aging group and translocated to the outer membrane of mitochondria, co‐regulating DRP1; thereby increasing mitochondrial fission. A significant reduction in the quality of mitochondria in the aging group, a serious imbalance, and a significant reduction in energy, causing metabolism shift toward glycolysis, were also reported. Since PGAM5 is eliminated, the mitochondrial function and metabolism of aging cells are partially reversed. A total of 70 patients undergoing in vitro fertilization (IVF) treatment were recruited in this clinical study. The high expression of PGAM5 in the cumulus cells is negatively correlated with the pregnancy rate of infertile patients. Hence, PGAM5 has immense potential to be used as a diagnostic marker.

Oocyte mitochondria – Key regulators of oocyte function and potential therapeutic targets for improving fertility

The development of oocytes and early embryos is dependent on mitochondrial ATP production. This reliance on mitochondrial activity, together with the exclusively maternal inheritance of mitochondria in development, places mitochondria as central regulators of both fertility and transgenerational inheritance mechanisms. Mitochondrial mass and mtDNA content massively increase during oocyte growth. They are highly dynamic organelles and oocyte maturation is accompanied by mitochondrial trafficking around subcellular compartments. Due to their key roles in generation of ATP and reactive oxygen species, oocyte mitochondrial defects have largely been linked with energy deficiency and oxidative stress. Pharmacological treatments and mitochondrial supplementation have been proposed to improve oocyte quality and fertility by enhancing ATP generation and reducing reactive oxygen species levels. More recently, the role of mitochondria-derived metabolites in controlling epigenetic modifiers has provided a mechanistic basis for mitochondria-nuclear crosstalk, allowing adaptation of gene expression to specific metabolic states. Here, we discuss the multi-faceted mechanisms by which mitochondrial function influence oocyte quality, as well as longer-term developmental events within and across generations.

Mitofusins: from mitochondria to fertility

Germ cell formation and embryonic development require ATP synthesized by mitochondria. The dynamic system of the mitochondria, and in particular, the fusion of mitochondria, are essential for the generation of energy. Mitofusin1 and mitofusin2, the homologues of Fuzzy onions in yeast and Drosophila, are critical regulators of mitochondrial fusion in mammalian cells. Since their discovery mitofusins (Mfns) have been the source of significant interest as key influencers of mitochondrial dynamics, including membrane fusion, mitochondrial distribution, and the interaction with other organelles. Emerging evidence has revealed significant insight into the role of Mfns in germ cell formation and embryonic development, as well as the high incidence of reproductive diseases such as asthenospermia, polycystic ovary syndrome, and gestational diabetes mellitus. Here, we describe the key mechanisms of Mfns in mitochondrial dynamics, focusing particularly on the role of Mfns in the regulation of mammalian fertility, including spermatogenesis, oocyte maturation, and embryonic development. We also highlight the role of Mfns in certain diseases associated with the reproductive system and their potential as therapeutic targets.

Melatonin improves the quality of maternally aged oocytes by maintaining intercellular communication and antioxidant metabolite supply

In mammalian ovaries, oocytes are physically coupled to somatic granulosa cells, and this coupling is crucial for the growth and development of competent oocytes as it mediates the transfer of metabolic support molecules. However, aging-mediated dysregulation in communication between the oocytes and granulosa cells affects the oocyte quality. In the present study, we examined the defected germline-soma communication and reduced mRNA levels encoding key structural components of transzonal projections (TZPs) in maternally aged oocytes. Oral administration of melatonin to aged mice substantially increased TZPs and maintained the cumulus cells-oocyte communication, which played a central role in the production of adequate oocyte ATP levels and reducing the accumulation of reactive oxygen species (ROS), apoptosis, DNA damage, endoplasmic reticulum (ER) stress and spindle/chromosomal defects. This beneficial effect of melatonin was inhibited by carbenoxolone (CBX), a gap junctional uncoupler, which disrupts bidirectional communications between oocyte and somatic cells. Simultaneously, melatonin significantly increased the mRNA and protein levels corresponding to genes associated with TZPs and prevented TZP retraction in in vitro-cultured cumulus-oocyte complex (COCs). Furthermore, we infused melatonin and CBX into the COCs in vitro culture system and monitored the levels of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH) in cumulus cells and oocytes. Notably, COCs treated with melatonin demonstrated improved NADPH and GSH levels. Of note, CBX was capable of reducing NADPH and GSH levels, aggravated the ROS accumulation and ER stress. Collectively, our data demonstrate the role of melatonin in preventing age-associated germline-soma communication defects, aiding the relay of antioxidant metabolic molecules for the maintenance of oocyte quality from cumulus cells, which have important potential for improving deficient phenotypes of maternally aged oocytes and the treatment of woman infertility.

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Communication between the oocytes and cumulus cells declines with age.

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Melatonin repair of aging-induced dysregulation in communication between the oocytes and cumulus cells.

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Melatonin preventing age-associated metabolic co-dependence defects of oocytes and cumulus cells.

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Melatonin attenuates mitochondrial dysfunction and endoplasmic reticulum stress.

Uncovering the important role of mitochondrial dynamics in oogenesis: impact on fertility and metabolic disorder transmission

Oocyte health is tightly tied to mitochondria given their role in energy production, metabolite supply, calcium (Ca2+) buffering, and cell death regulation, among others. In turn, mitochondrial function strongly relies on these organelle dynamics once cyclic events of fusion and fission (division) are required for mitochondrial turnover, positioning, content homogenization, metabolic flexibility, interaction with subcellular compartments, etc. Importantly, during oogenesis, mitochondria change their architecture from an "orthodox" elongated shape characterized by the presence of numerous transversely oriented cristae to a round-to-oval morphology containing arched and concentrically arranged cristae. This, along with evidence showing that mitochondrial function is kept quiescent during most part of oocyte development, suggests an important role of mitochondrial dynamics in oogenesis. To investigate this, recent works have downregulated/upregulated in oocytes the expression of key effectors of mitochondrial dynamics, including mitofusins 1 (MFN1) and 2 (MFN2) and the dynamin-related protein 1 (DRP1). As a result, both MFN1 and DRP1 were found to be essential to oogenesis and fertility, while MFN2 deletion led to offspring with increased weight gain and glucose intolerance. Curiously, neither MFN1/MFN2 deficiency nor DRP1 overexpression enhanced mitochondrial fragmentation, indicating that mitochondrial size is strictly regulated in oocytes. Therefore, the present work seeks to discuss the role of mitochondria in supporting oogenesis as well as recent findings connecting defective mitochondrial dynamics in oocytes with infertility and transmission of metabolic disorders.

Melatonin reverses mitochondria dysfunction and oxidative stress-induced apoptosis of Sudan I-exposed mouse oocytes

Sudan I is one of the industry dyes and widely used in cosmetics, wax agent, solvent and textile. Sudan I has multiple toxicity such as carcinogenicity, mutagenicity, genotoxicity and oxidative damage. However, Sudan I has been illegally used as colorant in food products, triggering worldwide attention about food safety. Nevertheless, the toxicity of Sudan I on reproduction, particularly on oocyte maturation is still unclear. In the present study, using mouse in vivo models, we report the toxicity effects of Sudan I on mouse oocyte. The results reflect that Sudan I exposure disrupts spindle organization and chromosomes alignment as well as cortical actin distribution, thus leading to the failure of polar body extrusion. Based on the transcriptome results, it is found that the exposure of Sudan I leads to the change in expression of 764 genes. Moreover, it's further reflected that the damaging effects of Sudan I are mediated by the destruction of mitochondrial functions, which induces the accumulated ROS to stimulate oxidative stress-induced apoptosis. As an endogenous hormone, melatonin within the ovarian follicle plays function on improving oocyte quality and female reproduction by efficiently suppressing oxidative stress. Moreover, melatonin supplementation also improves oocyte quality and increases fertilization rate during in vitro culture. Consistent with these, we find that in vivo supplementation of melatonin efficaciously suppresses mitochondrial dysfunction and the accompanying apoptosis, thus reverses oocyte meiotic deteriorations. Collectively, our results prove the reproduction toxicity of Sudan I for the exposure of Sudan I reduces the oocyte quality, and demonstrate the protective effects of melatonin against Sudan I-induced meiotic deteriorations.

Hexestrol Deteriorates Oocyte Quality via Perturbation of Mitochondrial Dynamics and Function

Hexestrol (HES) is a synthetic non-steroidal estrogen that was widely used illegally to boost the growth rate in livestock production and aquaculture. HES can also be transferred to humans from treated animals and the environment. HES has been shown to have an adverse effect on ovarian function and oogenesis, but the potential mechanism has not been clearly defined. To understand the potential mechanisms regarding how HES affect female ovarian function, we assessed oocyte quality by examining the critical events during oocyte maturation. We found that HES has an adverse effect on oocyte quality, indicated by the decreased capacity of oocyte maturation and early embryo development competency. Specifically, HES-exposed oocytes exhibited aberrant microtubule nucleation and spindle assembly, resulting in meiotic arrest. In addition, HES exposure disrupted mitochondrial distribution and the balance of mitochondrial fission and fusion, leading to aberrant mitochondrial membrane potential and accumulation of reactive oxygen species. Lastly, we found that HES exposure can increase cytosolic Ca²⁺ levels and induce DNA damage and early apoptosis. In summary, these results demonstrate that mitochondrial dysfunction and perturbation of normal mitochondrial fission and fusion dynamics could be major causes of reduced oocyte quality after HES exposure.

Oxidative stress in oocyte aging and female reproduction

In a healthy body, reactive oxygen species (ROS) and antioxidants remain balanced. When the balance is broken toward an overabundance of ROS, oxidative stress appears and may lead to oocyte aging. Oocyte aging is mainly reflected as the gradual decrease of oocyte quantity and quality. Here, we aim to review the relationship between oxidative stress and oocyte aging. First, we introduced that the defective mitochondria, the age-related ovarian aging, the repeated ovulation, and the high-oxygen environment were the ovarian sources of ROS in vivo and in vitro. And we also introduced other sources of ROS accumulation in ovaries, such as overweight and unhealthy lifestyles. Then, we figured that oxidative stress may act as the "initiator" for oocyte aging and reproductive pathology, which specifically causes follicular abnormally atresia, abnormal meiosis, lower fertilization rate, delayed embryonic development, and reproductive disease, including polycystic ovary syndrome and ovary endometriosis cyst. Finally, we discussed current strategies for delaying oocyte aging. We introduced three autophagy antioxidant pathways like Beclin-VPS34-Atg14, adenosine 5'-monophosphate (AMP)-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR), and p62-Keap1-Nrf2. And we also describe the different antioxidants used to combat oocyte aging. In addition, the hypoxic (5% O₂ ) culture environment for oocytes avoiding oxidative stress in vitro. So, this review not only contribute to our general understanding of oxidative stress and oocyte aging but also lay the foundations for the therapies to treat premature ovarian failure and oocyte aging in women.

Nicotinamide Mononucleotide Supplementation Reverses the Declining Quality of Maternally Aged Oocytes

Advanced maternal age is highly associated with a decline in oocyte quality, but effective approaches to improve it have still not been fully determined. Here, we report that in vivo supplementation of nicotinamide mononucleotide (NMN) efficaciously improves the quality of oocytes from naturally aged mice by recovering nicotinamide adenine dinucleotide (NAD⁺) levels. NMN supplementation not only increases ovulation of aged oocytes but also enhances their meiotic competency and fertilization ability by maintaining the normal spindle/chromosome structure and the dynamics of the cortical granule component ovastacin. Moreover, single-cell transcriptome analysis shows that the beneficial effect of NMN on aged oocytes is mediated by restoration of mitochondrial function, eliminating the accumulated ROS to suppress apoptosis. Collectively, our data reveal that NMN supplementation is a feasible approach to protect oocytes from advanced maternal age-related deterioration, contributing to the improvement of reproductive outcome of aged women and assisted reproductive technology.

MFN2 interacts with nuage-associated proteins and is essential for male germ cell development by controlling mRNA fate during spermatogenesis

Mitochondria play a crucial role in spermatogenesis and are regulated by several mitochondrial fusion proteins. However, their functional importance associated with their structure formation and mRNA fate regulation during spermatogenesis remains unclear. Here, we show that mitofusin 2 (MFN2), a mitochondrial fusion protein, interacts with nuage-associated proteins (including MIWI, DDX4, TDRKH and GASZ) in mice. Conditional mutation of Mfn2 in postnatal germ cells results in male sterility due to germ cell developmental defects. Moreover, MFN2 interacts with MFN1, another mitochondrial fusion protein with a high-sequence similarity to MFN2, in testes to facilitate spermatogenesis. Simultaneous mutation of Mfn1 and Mfn2 in testes causes very severe infertile phenotypes. Importantly, we show that MFN2 is enriched in polysome fractions of testes and interacts with MSY2, a germ cell-specific DNA/RNA-binding protein, to control gamete-specific mRNA (such as Spata19) translational activity during spermatogenesis. Collectively, our findings demonstrate that MFN2 interacts with nuage-associated proteins and MSY2 to regulate male germ cell development by controlling several gamete-specific mRNA fates.

Increase of mitochondria surrounding spindle causes mouse oocytes arrested at metaphase I stage

During oocyte meiosis, mitochondria usually surround spindle to meet the energy demand of spindle migration and chromosome segregation. Therefore, the mitochondrion surrounding spindle is widely accepted as an important indicator to demonstrate the mitochondrial function in oocyte studies. However, the role of mitochondria surrounding spindle in oocyte quality is not exactly addressed. Mitofusin-2 (MFN2) is a mitochondrial outer membrane GTPase that mediates mitochondrial clustering and fusion. Here, we increased the mitochondria surrounding spindle by overexpression of MFN2 in mouse oocytes. Results indicate that the increase of mitochondria surrounding spindle has little effect on germinal vesicle breakdown (GVBD), spindle migration, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) production and Endoplasmic reticulum (ER) distribution, while blocks chromosome segregation, destroys the spindle, and finally causes most of the oocytes to arrest at metaphase I stage. Collectively, our results demonstrate the mitochondria surrounding spindle is precisely regulated during oocyte maturation, while too much of it may cause abnormal oocyte meiosis. Therefore, although mitochondrion surrounding spindle is a typical biological event during oocyte maturation, utilizing it to demonstrate the mitochondrial function and oocyte quality should be much careful.

Maternal transmission of mitochondrial diseases

Given the major role of the mitochondrion in cellular homeostasis, dysfunctions of this organelle may lead to several common diseases in humans. Among these, maternal diseases linked to mitochondrial DNA (mtDNA) mutations are of special interest due to the unclear pattern of mitochondrial inheritance. Multiple copies of mtDNA are present in a cell, each encoding for 37 genes essential for mitochondrial function. In cases of mtDNA mutations, mitochondrial malfunctioning relies on mutation load, as mutant and wild-type molecules may co-exist within the cell. Since the mutation load associated with disease manifestation varies for different mutations and tissues, it is hard to predict the progeny phenotype based on mutation load in the progenitor. In addition, poorly understood mechanisms act in the female germline to prevent the accumulation of deleterious mtDNA in the following generations. In this review, we outline basic aspects of mitochondrial inheritance in mammals and how they may lead to maternally-inherited diseases. Furthermore, we discuss potential therapeutic strategies for these diseases, which may be used in the future to prevent their transmission.

Mitochondrial dynamics and interorganellar communication in the development and dysmorphism of mammalian oocytes

Mitochondria play many critical roles in cells, not only by supplying energy, but also by supplying metabolites, buffering Ca2+ levels and regulating apoptosis. During oocyte maturation and subsequent embryo development, mitochondria change their morphology by membrane fusion and fission, and coordinately undergo multiple cellular events with the endoplasmic reticulum (ER) closely apposed. Mitochondrial fusion and fission, known as mitochondrial dynamics, are regulated by family members of dynamin GTPases. Oocytes in animal models with these regulators artificially altered exhibit morphological abnormalities in nearby mitochondria and at the ER interface that are reminiscent of major cytoplasmic dysmorphisms in human assisted reproductive technology, in which a portion of mature oocytes retrieved from patients contain cytoplasmic dysmorphisms associated with mitochondria and ER abnormal morphologies. Understanding organelle morpho-homeostasis in oocytes obtained from animal models will contribute to the development of novel methods for determining oocyte health and for how to deal with dysmorphic oocytes.